CONFIG_TEXT: An erro occurred opening that folder on the FTP server. Make sure you have permission to access that folder. The operation timed out

or

CONFIG_TEXT: Error listing directory '/httpdocs'. Transfer channel can't be opened. Reason: No connection could be made because the target machine actively refused it. Could not retrieve directory listing

Note: Starting from Plesk Onyx, passive ports can be defined in /etc/proftpd.d/55-passive-ports.conf file.

The port range selected must be in the non-privileged range (e.g., greater than or equal to 1024); it is strongly recommended that the chosen range should be large enough to handle many simultaneous passive connections (for example, 49152-65534, the IANA-registered ephemeral port range).The port range should be allowed for incoming connections in the server firewall settings. Contact a server administrator to configure it if required.